1. Technical Field
The present invention relates to a filling process and more particularly to a filling process for automatically filling dual fluid cartridge assemblies.
2. Description of the Prior Art
Fluid cartridge assemblies are generally known in the art. Both single and multiple fluid cartridge assemblies are known. An example of a single fluid cartridge assembly is disclosed in commonly owned international patent application number PCT/US02/39041, filed on Dec. 6, 2002. Such a fluid cartridge assembly is used to dispense a single fluid.
Dual fluid cartridge assemblies are also known. Examples of such dual fluid cartridge assemblies are disclosed in U.S. Pat. Nos. 4,220,261; 4,961,520; and 5,310,091. Such dual fluid cartridge assemblies are known to be used to dispense fluid materials, such as thermoset adhesives, which typically contain two fluids that need to remain separated and applied to a workpiece quickly after mixing.
U.S. Pat. No. 5,310,091 discloses a dual fluid cartridge assembly configured with a front and rear chamber formed by an inner cartridge and an outer cartridge, respectively. Upper and lower piston seals are used to separate the fluids within the cartridges. Movement of the inner cartridge, for example, under the influence of a plunger of a conventional caulking gun, causes the inner cartridge to advance axially within the outer cartridge. The inner cartridge is in fluid communication with a hollow delivery tube which extends through a front chamber up to a cartridge outlet nozzle. Movement of the inner cartridge within the outer cartridge causes fluids in the inner cartridge and outer cartridge to be dispensed.
A problem exists with filling such cartridges. In particular, it is normally necessary to bleed air from the cartridge to prevent air from being trapped within the cartridge during filling. Such trapped air is known to have a negative impact on the ability to control the volumetric ratio of the fluids dispensed. If air is trapped in the inner cartridge, for example, the initial movement of the piston seals and accompanying increase in pressure in the cartridge chamber will act will cause that air to be compressed rather than to force fluid out of the outlet of the cartridge. Therefore, as the pressure in the cartridge increases during the early phase of the dispensing cycle, a smaller amount of the fluid in the inner cartridge will be dispensed than is desired. As the pressure in the cartridge decreases later, the air still trapped in the inner cartridge will expand and cause a larger than desired amount of fluid to be dispensed from the inner cartridge during the later phase of the dispensing cycle. If a different amount of air is trapped in the outer cartridge, the air will compress and expand at different rates than that of the air in the inner cartridge chamber. The difference in these rates will cause variation in the ratio of the fluids dispensed from the two cartridge chambers. This variation may have a negative impact on the performance of the fluids to be mixed.
To avoid this problem, various methods are known for removing air from the cartridge chambers after filling, during piston insertion. For example, shims or wires are known to be automatically inserted adjacent the piston seal prior to piston insertion and used as a method for bleeding air from the cartridge. The shims are removed after the pistons are inserted. This method is known to be used with relatively high viscosity fluids.
Unfortunately, there are several problems associated with this method. First, the shims can become fouled by way of contact with a fluid, thus eliminating or reducing the effectiveness of the shims. Second, the shims and wires are prone to breaking and curling due to their relatively small cross sections. Third, such shims and wires must be replaced periodically. Fourth, burrs and sharp edges along the length of the shims are known to damage the piston seal and thus affect its performance. Lastly, the use of wires or shims requires extra steps and thus increases the cost of filling the cartridge assembly.
Another known method for removing air from a cartridge before filling is use of a vacuum. Unfortunately, since it takes time to draw a vacuum, this approach increases the time required to fill the cartridge.
Finally, some systems are known to employ bleed plugs which include a vent for allowing air to escape. With this type of system, the vent is plugged after all of the air has been expelled between the piston and fluid within the cartridge. Unfortunately, such systems require additional steps and components and thus increase the time and cost of filling such cartridges. Thus, there is a need for a cartridge filling method which allows the cartridges to be filled quickly and easily while bleeding air from the cartridges without the need for extra steps or the need for a vacuum.